St James's Palace and Clarence House confirmed yesterday (December 3) that the young royal couple were expecting their first child together, releasing the statement: "The Queen, The Duke of Edinburgh, The Prince of Wales, The Duchess of Cornwall and Prince Harry and members of both families are delighted with the news.
"The Duchess was admitted this afternoon to King Edward VII Hospital in Central London with Hyperemesis Gravidarum [acute morning sickness].
"As the pregnancy is in its very early stages, Her Royal Highness is expected to stay in hospital for several days and will require a period of rest thereafter."
Catherine is believed to be less than 12 weeks pregnant and that her admission to hospital led to the announcement.
She's currently suffering from Hyperemesis Gravidarum, with retired midwife Val Clarke explaining the rare condition to Sky News: "It often happens in very slim young ladies who - I don't know the reason why - become pregnant and the demands of the pregnancy are overwhelming to the point that vomiting becomes much more severe much earlier.
"I admire Kate. She was playing hockey, she may have been feeling awful, but she put on a very good show for everybody. But now I think she needs to tend to her own wellbeing and that of the baby."
The 30-year-old Duchess was playing hockey last week after she returned to her old school in Pangbourne.
The hospital is currently being guarded by police with the world's press gathered outside.
See pictures of the Duchess of Cambridge and Prince William together over the last two years here: